Copolymers of polyaspartic acid

ABSTRACT

Higher molecular weight copolymers of polyaspartic acid which are suitable for the inhibition of scale deposition may be obtained by reacting maleic acid and ammonia in a stoichiometric excess, with a diamine or a triamine, at 120°-350° C., preferably 180°-300° C., and then converting the copolymer of polysuccinimide formed to a salt of a copolymer of polyaspartic acid by hydrolysis with a hydroxide.

This application is a division of application Ser. No. 08/373,088, filedJan 17, 1995 now U.S. Pat. No. 5,466,760, pending; Ser. No. 08/261,425,filed Jun. 17, 1994, now U.S. Pat. No. 5,391,642; Ser. No. 08/195,036,filed Feb. 14, 1994, now U.S. Pat. No. 5,357,004; Ser. No. 08/044,900,filed Apr. 7, 1993, now U.S. Pat. No. 5,285,810; Ser. No. 07/926,242,filed Aug. 7, 1992, abandoned.

FIELD OF THE INVENTION

This invention relates to a process for the production of copolymers ofpolysuccinimide, their conversion to salts of copolymers of polyasparticacid and the use of these materials.

BACKGROUND OF THE INVENTION

The salts of polyaspartic acid have been used for fertilizers and scaleinhibition agents. They are particularly useful for the prevention ofscale deposition in boiler water, reverse osmosis membranes, detergentsand as Inhibitors of dental tartar and plaque formation (tartar barrieragents). These materials are readily biodegradable. Economic methods ofproduction of polyaspartic acid having a higher molecular weight isdesirable to provide materials having a greater retention on the objectwherein inhibition of scale deposition is desired, and to providegreater stability to biodegradation in addition to their intrinsic valuefor the prevention of scale deposition in boiler water, reverse osmosismembranes, detergents and as inhibitors of dental tartar and plaqueformation (tartar barrier agents).

Highly functionalized, yet readily biodegradable materials, whichfunction as inhibitors of scale deposition are desirable for use asfertilizers, in detergents, in water treatment, and in control oftartar.

The problem of obtaining higher molecular weight polymers of amino acidshas been given a great deal of thought due to the rapid degradation ofthese polymers, especially in the mouth. A major drawback to the use ofsuch polymers as antitartar agents is the lifetime that such polymershave in the mouth. Achieving a means by which a higher molecular weightagent can be obtained is desirable from both an economic and a usestandpoint.

DESCRIPTION OF RELATED ART

A number of methods of preparation of polyaspartic acid are disclosed inthe literature and other patents, however, no mention is made of methodsof preparation of copolymers of polyaspartic acid.

U.S. Pat. No. 4,839,461 discloses a method for making polyaspartic acidfrom maleic acid and ammonia by reacting these constituents in a 1:1-1.5molar ratio by raising the temperature to 120°-150° C. over a period of4-6 hours and maintaining it for 0-2 hours. It is further disclosed thattemperatures above 140° C. result in elimination of CO₂, thus teachingdegradation of the material. The molecular weight range obtained by thismethod was said to be 1,000-4,000 with a cluster at 1,800-2,000. It isfurther disclosed that this material is useful in the prevention oftarnishing on glass and porcelain articles. Although not stated, it isknown that this action would occur as a result of the inhibition ofdivalent metal ion salt deposition.

Harada, et al (Thermal polycondensation of free amino acids withpolyphosphoric acid. Origins Prebiol. systems Their Mol Matrices, Proc.Conf., Wakulla Springs, Fla., 289, 1963) obtained polysuccinimide fromaspartic acid and phosphoric acid at temperatures over 100° C. over atime period of 50-250 hrs, but required temperatures over 170° withoutphosphoric acid being present. Conventional alkaline hydrolysis providedpolyaspartic acid. No molecular weight range was given.

Sodium polyaspartate of 6000 molecular weight (MW) was used in theprevention of boiler scale by changing the crystal structure of calciumsalts resulting in the formation of a soft scale (Sarig et al, The useof polymers for retardation of scale formation. Natl Counc Res Dev Rep!(Isr.), 150, 1977). Polyaspartic acid was found to be superior topolyglutamate, MW 14,400, polyvinyl sulfonate, MW 5300, and polyacrylicacid, MW 6,000, in that it gave 66% retardation of total scale and 90%retardation of calcium sulfate scale. In addition, the scale formed inthe presence of polyaspartate was softer than that produced in thepresence of polyacrylate, polyglutamate and polyvinyl sulfonate.

U.S. Pat No. 5,057,597 discloses a method for the polycondensation ofaspartic acid to produce polyaspartic acid by heating the aspartic acidin a fluidized bed reactor to 221° C. for a period of 3-6 hours in anitrogen atmosphere followed by conventional alkaline hydrolysis.

Kovacs et al. (J. Org. Chem., 25 1084 1961!) prepared polyaspartic acidby heating aspartic acid to 200° C. in vacuo for a period of 120 hoursor in boiling tetralin over a period of 100 hours followed by alkalinehydrolysis. Kovacs et al, showed that the intermediate formed in thethermal polymerization of aspartic acid was polysuccinimide.

U.S. Pat. No. 3,856,380 discloses the preparation of derivatives ofpolyaspartic acid by reaction with a primary or secondary amine isreacted with polysuccinimide in a solvent such as dimethylformamide,diethylformamide or dimethylacetamide, followed by alkaline hydrolysis.

In a co-pending application, Ser. No. 07/882/919, incorporated herein byreference; a method of production of polyaspartic acid is disclosed inwhich maleic acid and ammonia are heated to 160°-300° C. followed byhydrolysis with a hydroxide.

The prior art does not disclose the synthesis of the high molecularweight copolymers of polyaspartic acid or the high molecular weightcopolymers of polysuccinimide of this invention.

SUMMARY OF THE INVENTION

High molecular weight copolymers of polysuccinimide were prepared byreacting maleic acid, ammonia and a polyamine at temperatures greaterthan 120° C. High molecular weight copolymers of polyaspartic acid wereprepared by hydrolyzing the polysuccinimide polymers with a hydroxide.

One object of this invention is to provide a means of preparingcopolymers of polysuccinimide. A further object of this invention is toprovide a means of preparing copolymers of polyaspartic acid. Yetanother object of this invention is to provide novel compositions whichare useful for the inhibition of salt deposition, especially bivalentmetal salts, whether in water treatment, detergent addition, oral healthcare or cosmetic formulation. Yet another object of this invention is toprovide novel compositions which may be further reacted to providecosmetically useful compounds.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Higher molecular weight copolymers of polyaspartic acid which aresuitable for the inhibition of scale deposition may be obtained byreacting maleic acid and ammonia in a stoichiometric excess, with acompounds having 2 or more primary or secondary amine groups permolecule, at 120°-350° C., preferably 180°-300° C., and then convertingthe copolymer of polysuccinimide formed to a salt of a copolymer ofpolyaspartic acid by hydrolysis with a hydroxide. The reaction iscarried out first by the addition of water to maleic anhydride, thusforming maleic acid, or to maleic acid itself, followed by addition ofthe appropriate amount of ammonia In the form of gaseous ammonia or asits aqueous solution. At this point, the polyamine is added. Thissolution is then heated to remove water. As water is removed, themixture becomes a solid and then a melt of the mixture is formed. Waterremoval continues as the reaction proceeds and the temperature isbrought to 120°-300° C. When the theoretical quantity of water formed inthe production of the copolymer of polysuccinimide has been removed,which, depending on the temperature, may occur in even less than 5minutes, the reaction mixture is allowed to cool. Typically, it may takeup to 8 hours at 120° C., whereas it may take less than 5 minutes at300° C. The copolymer of polysuccinimide formed can be used to makeother novel and useful products by reactions such as those described inU.S. Pat. No. 4,363,797, wherein useful derivatives for cosmetic use aredescribed or can be hydrolyzed with metal hydroxides to provide theappropriate salt of polyaspartic acid. Solutions of the salts of thecopolymers of polyaspartic acid formed in this manner have the samescale inhibition performance and molecular weight range as do thepolymers formed by the thermal polymerization of aspartic acid itself.Further manipulation to remove the water or the salts can be carried outto provide water free powders of the salts or the free acid.

Any polyamine may be used to produce these copolymers which has at leasttwo or more primary or secondary amines available for reaction.Preferred polyamines have at least two primary amine groups.

The copolymers of polyaspartic acid provided by the present inventionare advantageous for inhibition of scale deposition, especially where anincreased molecular weight is desirable to provide appropriatebiodegradability and retention on surfaces for preventing saltdeposition whether in water treatment, detergent additive, oral healthcare or cosmetic formulation.

These compounds may be used as additives to detergents, to cosmetics andhair treating compositions and to tooth paste. Although the exactmechanism of action of these compounds is not known, it is likely thatthese high molecular weight copolymers interfere with the crystalstructure of salt deposits. Such interference either prevents thedeposit of the salt or causes the formation of a soft crystal depositwhich is easily removed by water action.

EXAMPLE 1. Thermal Co-Polymerization of mono- Ammonium Maleate withamines

In each case the following procedure was carried out with the indicatedamine. A slurry of 19.6 g (0.2 mole) maleic anhydride was dissolved in40 ml water at 80°-95° C. and stirred for 30 minutes while allowing themixture to cool to 25° C. To this solution at 250° C. was added 30 g of30% aqueous solution of ammonium hydroxide (0.22 mol NH₃). Afterthorough mixing, the indicated amine was added in the quantity noted.This solution was evaporated to dryness over a period of 30 minutes. Thesolid was then heated at 200°-230° C. for 5 minutes, removed from theheat, allowed to cool and broken up with a spatula. The solid was thenheated at 235°-245° C. for 10 minutes, removed from the heat, allowed tocool and broken up with a spatula. Finally, the solid was heated at235°-245° C. for 10-15 minutes, removed from the heat and allowed tocool to room temperature. The resulting water insoluble polymer wasslurried in 40.0 ml of water and a solution of 7.6 g of sodium hydroxidein 12 ml of water was added over 5 minutes. The solution was stirred for10-20 minutes to give a clear red-brown solution, pH 10-11.0. JEFFAMINEis a trademark of Texaco Chemical Co. for its amines and these aminesare defined as follows:

JEFFAMINE T403, Mol. wt. 440, is a triamine made from trimethylolpropanewhich has been chain extended with propylene oxide and end-capped withprimary amines.

JEFFAMINE EDR 148, mol. wt. 148, is a diamine made from triethyleneglycol end capped with primary amines.

JEFFAMINE ED 600, mol. wt. 600, is a linear diamine made from acopolymer having approximately 13-14 oxyethylene units and 3-4oxypropylene units which are endcapped with primary amines.

The copolymer of sodium polyaspartate was tested for inhibition ofcalcium carbonate precipitation by the calcium drift assay. In thisassay a supersaturated solution of calcium carbonate is formed by adding0.3 ml of a sodium carbonate solution (0.25 M NaHCO₃ +0.25 M Na₂ CO₃) to29.1 ml of 0.55 M NaCl and 0.01 M KCl containing 0.15 ml of 1.0 M CaCl₂and 1.7 ppm of the material to be tested. The reaction is initiated byadjusting the pH to 7.5-8.5 by titration with 1 N NaOH and addition ofthe material to be tested for inhibition of CaCO₃ precipitation at alevel of 1.7 ppm. At three minutes, the reaction is seeded by theaddition of 10 mg of CaCO₃ and the pH is recorded. The decrease in pH isdirectly correlated to the amount of CaCO₃ that precipitates. Betterinhibitors show lower changes in pH. The effectiveness of the inhibitionis compared to that of sodium polyacrylate, used commercially for thepurpose of preventing scale formation.

Table 1 shows the molecular weight measurements, which are given as thetime in minutes for the elution of the maximum peak height upon gelpermeation chromatography (GPC) of 0.1 to 0.5 mg of each sampledissolved in 8 ml of the aqueous mobile phase. The GPC conditions were:column 1 cm×17.5 cm (15 ml vol), Sephadex G50; aqueous phase of 0.02 MNa₂ HPO₄ /H₃ PO₄ adjusted to pH 7.0; flow rate of 0.5 ml/min at 250° C.;detected by UV at 240 nm. The molecular weight standards were aprotinin,6500 m.w., which eluted at 29 min and poly(sodium L-aspartate), 15,000m.w. which eluted at 17 minutes.

Table 1 shows the results of these tests with the materials prepared bythe method of this Example. The CaCO₃ drift values are calculated bysubtracting the pH recorded at 20 minutes from the pH recorded at 3minutes. The yield given is that of polysuccinimide.

                                      TABLE 1    __________________________________________________________________________                         Weight of  CaCO.sub.3                                          mol. wt.                         amine  Yield                                    Drift peak    Sample        Amine Added Type (g)                            (moles)                                (g) (pH units)                                          (min)    __________________________________________________________________________    none                            0.95    384-2        none                    19.5                                    0.29  20.5    5000 mol. wt. polyacrylate      0.10    2000 mol. wt. polyacrylate      0.24    375-2        diethyiene triamine                    diamine                         0.5                            .0048                                20.3                                    0.21  20.6    375-4        diethylene triamine                    diamine                         1.5                            .0014                                20.7                                    0.22  16    375-6        diethylene triamine                    diamine                         2.5                            .0024                                21.2                                    0.21  16    367-2        JEFFAMINE T-403                    triamine                         1.44                            .003                                21.4                                    0.31  15.5    367-8        JEFFAMINE T-403                    triamine                         2.1                            .0048                                21.3                                    0.27  15    367-6        JEFFAMINE T-403                    triamine                         2.88                            .006                                21.2                                    gelled    377-2        melamine    triamine                         0.6                            .0048                                20.0                                    0.31  24.5    374-2        JEFFAMINE EDR 148                    diamine                         1.06                            .007                                20.3                                    0.20  15.5    374-4        JEFFAMINE EDR 148                    diamine                         3.18                            .021                                22.1                                    gelled    381-2        JEFFAMINE ED600                    diamine                         4.3                            .007                                23.3                                    0.25  16    382-2        ethylene diamine                    diamine                         0.43                            .007                                19.7                                    0.27  22    382-4        ethylene diamine                    diamine                         1.29                            .022                                20.1                                     .26  18    382-6        ethylene diamine                    diamine                         2.15                            .0358                                20.9                                    0.36  20    383-2        ethylene diamine                    diamine                         3.0                            .05 21.6                                    0.38  16.5    392-2        hexanediamine                    diamine                         1.6                            .014                                20.9                                    0.42  13.9    __________________________________________________________________________

EXAMPLE 2 Thermal Co-Polymerization of di-Ammonium Maleate with amines.

In each case the following procedure was carried out with the indicatedamine. A slurry of 23.2 g (0.2 mole) maleic acid was dissolved in 40 mlwater at 80°-95° C. and stirred for 30 minutes while allowing themixture to cool to 25° C. To this solution at 25° C. was added 60 g of30% aqueous solution of ammonium hydroxide (0.44 mol NH₃). Afterthorough mixing, the indicated amine was added in the quantity noted.This solution was evaporated to dryness over a period of 30 minutes. Thesolid was then heated at 200°-230° C. for 5 minutes, removed from theheat, allowed to cool and broken up with a spatula. The solid was thenheated at 235°-245° C. for 10 minutes, removed from the heat, allowed tocool and broken up with a spatula. Finally, the solid was heated at235°-245° C. for 10-15 minutes, removed from the heat and allowed tocool to room temperature. The resulting water insoluble polymer wasslurried in 40.0 ml of water and a solution of 7.6 g of sodium hydroxidein 12 ml of water was added over 5 minutes. The solution was stirred for10-20 minutes to give a clear red-brown solution, pH 10-11.0 was formed.The results of the resulting polymers were tested for calcium carbonateprecipitation and molecular weight as in Example 1.

                  TABLE 2    ______________________________________                                      CaCO.sub.3                      Weight of       Drift mol. wt.    Sam- Amine        amine     Yield (pH   peak    ple  Added     Type   (g) (moles)                                    (g)   units)                                                (min)    ______________________________________    none                            0.95    384-2         none               19.5    0.29  20.5    5000 mol. wt. polyacrylate                            0.10    2000 mol. wt. polyacrylate                            0.24    394-2         diethylene                   dia-   0.5 .0048 19.6  0.33  21         triamine  mine    ______________________________________

EXAMPLE 3 Reaction of aspartic acid with amines.

In each case the following procedure was carried out with the indicatedamine. A slurry of 26.6 g (0.2 mole) aspartic acid was dissolved in 40ml water. To this solution at 25° C. was added the indicated amine inthe quantity noted. This solution was evaporated to dryness over aperiod of 30 minutes. The solid was then heated at 235°-245° C. for 30minutes, removed from the heat, allowed to cool and broken up with aspatula. The solid was then heated at 235°-245° C. for 30 minutes,removed from the heat, allowed to cool and broken up with a spatula.Finally, the solid was heated at 235°-245° C. for 30 minutes, removedfrom the heat and allowed to cool to room temperature. The resultingwater insoluble polymer was slurried in 40.0 ml of water and a solutionof 7.6 g of sodium hydroxide in 12 ml of water was added over 5 minutes.The solution was stirred for 10-20 minutes to give a clear reddish-brownsolution, pH 10-11.0 was formed. The results of the tests described inExample 1 for these materials are given in Table 3.

                  TABLE 3    ______________________________________                                      CaCO.sub.3                      Weight of       Drift mol. wt.    Sam- Amine        amine     Yield (pH   peak    ple  Added     Type   (g) (moles)                                    (g)   units)                                                (min)    ______________________________________    none                            0.95    398-6         none               19.5    0.21  19    5000 mol. wt. polyacrylate                            0.10    2000 mol. wt. polyacrylate                            0.24    398-4         diethylene-                   dia-   .1  .001  19.5  0.21  19         triamine  mine    ______________________________________

It will be apparent to those skilled in the art that the examples andembodiments described herein are by way of illustration and not oflimitation, ant that other examples may be utilized without departingfrom the spirit and scope of the present invention, as set forth in theappended claims.

I claim:
 1. A process for the preparation of copolymers of polyasparticacid comprising reacting maleic acid, ammonia and a polyamine at atemperature of 120° C. to 350° C. and converting the resultant polymerinto a salt by adding a hydroxide.
 2. The process of claim 1 wherein thepolyamine has at least one primary amine and wherein the additionalamine groups consist of at least one primary or secondary amine.
 3. Theprocess of claim 1 wherein the polyamine is selected from the groupconsisting of diethylene triamine, a polyoxyalkyleneamine diamine ortriamine, melamine, an alkyl diamine or triamine, ethylene diamine andhexanediamine.